T8966: add legacy-label escape to invalid-task-id rule (commit check exempt)

[andamasov]

Adds a maintainer-controlled legacy label escape to the per-repo T-ID rule (toggles invalid-task-id). The PR title check stays enforced for every PR; the per-commit check is exempted when a PR carries the legacy label — an escape hatch for grandfathered PRs whose commit history cannot be rewritten (repos that squash-merge and block force-push). Pilot verified on vyos/vyos.vyos. Change-management: IS-539. Tracked under T8966.

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository YAML (base), Central YAML (inherited), Organization UI (inherited)

Review profile: CHILL

Plan: Pro

Run ID: 820c983e-a33e-4dad-aa06-5d1eae223524

📥 Commits

Reviewing files that changed from the base of the PR and between e018142 and 353e66c.

📒 Files selected for processing (1)

• .github/mergify.yml

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📝 Walkthrough

Summary by CodeRabbit

• Chores
  • Updated PR validation rules to exclude legacy-labeled pull requests from commit message format enforcement.

Walkthrough

Mergify rule for commit-message T-ID format validation updated to exclude PRs with the legacy label. The existing negative-regex check remains unchanged but is now combined with a label!=legacy condition in an and: block.

Changes

Mergify Rule Configuration

Layer / File(s)	Summary
T-ID format rule legacy exclusion .github/mergify.yml	The "Flag product T-ID format violation" rule condition is refactored to exclude PRs labeled legacy by wrapping the existing commit-message pattern check inside an and: condition alongside label!=legacy.

Possibly related PRs

• vyos/vyos-cloud-init#110: Both PRs modify .github/mergify.yml to handle the invalid-task-id label in relation to T-ID title/commit checks; the main PR gates this rule with label!=legacy.
• vyos/vyos-cloud-init#101: Modifies .github/mergify.yml Mergify rule configuration for PR enforcement, including T-ID format checks that this PR now gates.

✨ Finishing Touches

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch feat/T8966-legacy-escape

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